Influence of varying degree of salinity-sodicity stress on enzyme activities and bacterial populations of coastal soils of Yellow Sea, South Korea.

To study the effects of salinity-sodicity on bacterial population and enzyme activities, soil samples were collected from the Bay of Yellow Sea, Incheon, South Korea. In the soils nearest to the coastline, pH, electrical conductivity (ECe), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) were greater than the criteria of salinesodic soil, and soils collected from sites 1.5-2 km away from the coastline were not substantially affected by the intrusion and spray of seawater. Halotolerant bacteria showed similar trends, whereas non-tolerant bacteria and enzymatic activities had opposite trends. Significant positive correlations were found between EC, exchangeable Na+, and pH with SAR and ESP. In contrast, ECe, SAR, ESP, and exchangeable Na+ exhibited significant negative correlations with bacterial populations and enzyme activities. The results of this study indicate that the soil chemical variables related with salinity-sodicity are significantly related with the sampling distance from the coastline and are the key stress factors, which greatly affect microbial and biochemical properties.

Thiosulfate Oxidation and mixotrophic growth of Methylobacterium goesingense and Methylobacterium fujisawaense.

The mixotrophic growth with methanol plus thiosulfate was examined in nutrient-limited mixotrophic condition for Methylobacterium goesingense CBMB5 and Methylobacterium fujisawaense CBMB37. Thiosulfate oxidation increased the growth and protein yield in mixotrophic medium that contained 150 mM methanol and 20 mM sodium thiosulfate, at 144 h. Respirometric study revealed that thiosulfate was the most preferable reduced inorganic sulfur source, followed by sulfite and sulfur. M. goesingense CBMB5 and M. fujisawaense CBMB37 oxidized thiosulfate directly to sulfate, and intermediate products of thiosulfate oxidation such as polythionates, sulfite, and sulfur were not detected in spent medium and they did not yield positive amplification for tested soxB primers. Enzymes of thiosulfate oxidation such as rhodanese and sulfite oxidase activities were detected in cell-free extracts of M. goesingense CBMB5, and M. fujisawaense CBMB37, and thiosulfate oxidase (tetrathionate synthase) activity was not observed. It indicated that both the organisms use the "non-S4 intermediate" sulfur oxidation pathway for thiosulfate oxidation. It is concluded from this study that M. goesingense CBMB5, and M. fujisawaense CBMB37 exhibited mixotrophic metabolism in medium containing methanol plus thiosulfate and that thiosulfate oxidation and the presence of a "Paracoccus sulfur oxidation" (PSO) pathway in methylotrophic bacteria are species dependant.

Zinc metal solubilization by Gluconacetobacter diazotrophicus and induction of pleomorphic cells.

Gluconacetobacter diazotrophicus strain PAl5 exhibited a minimum inhibitory concentration value of 11 mM in an LGI medium amended with ZnCl2. When an LGI medium was amended with Zn metal, solubilization halos were observed in a plate assay, and further solubilization was confirmed in a broth assay. The maximum solubilization was recorded after 120 h with a 0.1% Zn metal amendment. During solubilization, the culture growth and pH of the broth were indirectly correlated. Using a Fourier Transform Infrared Spectroscopy analysis, one of the agents solubilizing the Zn metal was identified as gluconic acid. When the Zn-amended broth was observed under a bright field microscope, long involution cells were observed, and further analysis with Atomic Force Microscopy revealed highly deformed, pleomorphic, aggregate-like cells.

Thiosulfate oxidation and mixotrophic growth of Methylobacterium oryzae.

Thiosulfate oxidation and mixotrophic growth with succinate or methanol plus thiosulfate was examined in nutrient-limited mixotrophic condition for Methylobacterium oryzae CBMB20, which was recently characterized and reported as a novel species isolated from rice. Methylobacterium oryzae was able to utilize thiosulfate in the presence of sulfate. Thiosulfate oxidation increased the protein yield by 25% in mixotrophic medium containing 18.5 mmol.L-1 of sodium succinate and 20 mmol.L-1 of sodium thiosulfate on day 5. The respirometric study revealed that thiosulfate was the most preferable reduced inorganic sulfur source, followed by sulfur and sulfite. Thiosulfate was predominantly oxidized to sulfate and intermediate products of thiosulfate oxidation, such as tetrathionate, trithionate, polythionate, and sulfur, were not detected in spent medium. It indicated that bacterium use the non-S4 intermediate sulfur oxidation pathway for thiosulfate oxidation. Thiosulfate oxidation enzymes, such as rhodanese and sulfite oxidase activities appeared to be constitutively expressed, but activity increased during growth on thiosulfate. No thiosulfate oxidase (tetrathionate synthase) activity was detected.

Estimating nitrogen and phosphorus contents using model integrated in small agricultural watersheds.

The Agricultural Nonpoint Source Pollution Model (AGNPS) was applied to estimate the loads of nitrogen and phosphorus according to antecedent soil moisture conditions (AMC) using probable rainfall in a stream draining small agricultural watersheds. Calibration and verification of the model were performed using observed data collected from rainfall events in the Imgo watersheds during 1997-1998. Evaluation of model outputs was based on graphical displays contrasting observed and simulated values for each rainfall-runoff event, and standard statistics such as coefficient of efficiency. The coefficient of efficiency of peak flow, total N, and total P in the estimation were 0.97, 0.93, and 0.74, respectively. Probable rainfall of Imgo watersheds was computed for several return periods using the frequency analysis of Gumbel's extreme value distribution. As the probable flood increase, concentrations of total N and total P generally decrease. Loss of N and P was proportional to the preceding soil water content in the same probable rainfall. The excessive fertilization under AMC-III condition can cause relatively higher outflow of N and P from the soil. It can be concluded that surface runoff and sediment transport influence soil quality and the quality of water absorption and AGNPS can provide realistic estimates of nonpoint source nutrient yields.

Removal of organic matter and nitrogen from river water in a model floodplain.

A significant improvement in river water quality cannot be expected unless nonpoint-source contaminants are treated in addition to the further treatment of point-source contaminants. If river water is sprayed over a floodplain, the consequent water filtration through the sediment profile can simultaneously remove organic matter and nitrogen in the water through aerobic and denitrifying reactions. This hypothesis was tested using lysimeters constructed from polyvinyl chloride (PVC) pipe (150 cm long, 15 cm in diameter) packed with loamy sand floodplain sediment. Water was applied to the top of the lysimeters at three different flow rates (48, 54, and 68 mm d(-1)). Concentrations of NO3 and dissolved oxygen (DO), chemical oxygen demand (COD), and redox potential (Eh) in the water were measured as functions of depth after the system reached steady states for both water flow and reactions. At the rate of 68.0 mm d(-1), a reducing condition for denitrification developed below the 5-cm depth due to the depletion of O2 by organic matter degradation in the surface oxidizing layer; Eh and DO were below 205 mV and 0.4 mg L(-1), respectively. At a depth of 70 cm, COD and NO3-N concentration decreased to 5.2 and 3.8 mg L(-1) from the respective influent concentrations of 17.1 and 6.2 mg L(-1). Most biodegradable organic matter was removed during flow and further removal of NO3 was limited by the lack of an electron donor (i.e., organic matter). These results indicate that the floodplain filtration technique has great promise for treatment of contaminated river water.

Electron affinity coefficients of nitrogen oxides and biodegradation kinetics in denitrification of contaminated stream water.

During the dry season in Korea, rivers become more vulnerable to contamination by biochemical oxygen demand (BOD) and nitrogen. It is hypothesized that the natural characteristics of the streams in Korea allow the contaminated water to be treated at the tributaries. Down-stream river water quality in Korea may be improved by spraying the contaminated stream water from the tributaries over the surrounding floodplains. The consequent water filtration through the soil could remove the contaminants through aerobic and denitrifying reactions. In this study, the kinetics parameters of the denitrifying reaction in floodplain filtration were determined using contaminated stream water. For the electron donor the Monod kinetics was used, while the competitive Michaelis-Menten model was employed for the electron acceptors. The parameters to the competitive Michaelis-Menten model were found using continuous denitrifying reactions, instead of the batch reactions employed in previous studies, to match the conditions needed to apply the competitive Michaelis-Menten kinetics. From the result, it was found that continuous reactions as well as batch reactions could be used to determine the affinity coefficients in denitrification. The results of this study also showed that the affinity coefficient of NO2, using continuous reactions, was similar to that of other studies in the literature found via batch reactions, whereas the affinity coefficient of N2O was much larger than that acquired with batch reactions. The parameters obtained in this study will be used in future work to simulate the contaminant behaviors during floodplain filtration using a mathematical model.